1. Field of the Invention
The invention relates to a device for monitoring the pressure of a motor vehicle tire, where an actuator is employed for generating a regulating distance indicating a pressure drop in a measurement chamber.
2. Brief Description of the Background of the Invention Including Prior Art
Such a device is known from the German Patent DE-PS 2,813,058-C2. The device of the German Patent scans the tire pressure with a pressure-sensitive device, disposed at the vehicle wheel. Upon falling below specified tire pressure, the device actuates with this pressure sensitive device an actuator such that the actuator generates a regulating distance. An axially fixedly disposed sensor scans the position of the actuator and thereby recognizes a tire pressure, which is disposed below a preset or specified tire pressure. A corresponding information of the sensor can be fed via an evaluation circuit to a display unit, which is disposed, for example, in the driver's cab.
In case the tire pressure is equal to or higher than the specified tire pressure, corresponding to the constructive features of the pressure-sensitive device, no tire pressure is present at the actuator. Consequently, the actuator, subjected to the restoring force, is in an initial position, which is not associated with the display signal or, respectively, the sensor recognizes that the available tire pressure has not fallen below the specified set tire set pressure.
However, the actuator can also assume the above-recited non-indicating initial position if the tire pressure exerted onto the actuator has assumed such a low value, based on a marked drop in the tire pressure, that the restoring force directed opposite to the tire pressure prevails. The device of the German Patent is therefore associated with the disadvantage that the tire pressure monitoring is reliable only up to a certain minimum tire pressure, where the level of the minimum tire pressure is essentially determined by the restoring force directed to the actuator.
The German Patent DE-3,422,725-C2 to Rainer Achterholt teaches a valve cap with a pressure-decrease display for air tires. While the reference device is intended to indicate pressure changes in a tire, it does not provide a signal for a remote display of the pressure situation in a tire.
The German Patent Application Laid Open DE-OS 3,030,794-A1 to Philip Hugh Pegram teaches an air-loss warning device for an air tire. This reference teaches a view signal based on a pressure loss, however, no signal for a remote display is furnished by the reference structure.
The German Printed Patent Publication DE-OS 1,680,495 to Giacomo Spaggiari teaches a display device for pressure decreases in vehicle tires, in particular for motor vehicles. While the reference provides an indicator structure, this indicator structure is indirectly associated with the device and a remote display does not appear to be part of this structure.
The German Petit Patent G-8,206,932.8 to Wolfgang Lubs teaches a monitor for a filling volume. No possibility is given by this reference for a remote display of the indicated signal.
The German Printed Patent 820,545 to Josef Reiter et al. teaches a tire-pressure control device for air tires for tractors and their trailers. The reference aims at providing a display at a dashboard of the driver cabin. A strictly mechanical structure is taught in the reference, which appears quite unwieldy and impractical as described in the reference.